1. Field of the Invention
The present invention relates to clamps suitable for mounting devices at selected locations along rod-like members and, more particularly, relates to an improved wrap-around clamp which may be quickly yet safely utilized to mount theater lighting fixtures to structural tubulars.
2. Description of the Background
Clamps of various types have long been utilized to mount devices to structural members. In the entertainment industry, for example, theater lighting fixtures are frequently mounted by clamps to horizontal and/or vertical structural tubulars arranged in a grid. Lighting fixtures are usually remounted to different structural tubulars between various theatrical productions to obtain a preferred lighting for the scene. Each clamp typically remains secured to its lighting fixture, so that a light can be quickly removed from one fixed location and set at a new location by releasing the clamp from one tubular and refixing the clamp to a different tubular or to a different position along the same tubular. Once the clamp is positioned on the tubular with the lighting fixture merely being suspended therefrom, it is desired that the operator be able to delay for various reasons without fear of the fixture falling before the clamp is tightened or secured to the tubular to lock the lighting fixture at its desired position.
In many situations, clamps provide the preferred structural connection between the item to be mounted and the structural tubular. In addition to the ease and speed of removing and remounting the device, the clamp should provide a high degree of safety, so that the mounted device will not fall, either when the clamp is loosely secured about the tubular so that the device is "hung" from a horizontal tubular (if the type of clamp so permits), and/or after the clamp is completely affixed to the structural tubular with the device at its desired orientation. Furthermore, it is desirable that a clamp may be used to mount the same device to structural tubulars of various diameters, is light weight, is relatively inexpensive to manufacture, and may be quickly and reliably used even by newly trained personnel.
One type of clamp used to mount theater lighting fixtures to structural tubulars is a C-clamp, which hooks over a horizontal tubular, and has a post extending downward from the lower portion of the C-shaped body for securing to the lighting fixture. A bolt is threaded to the body and projects generally upward to engage the tubular and fix the clamp body to the tubular. While this type of C-clamp may be used with tubulars of different sizes, the clamp can only be used for securing relatively light-weight fixtures, and the fixture position is practically limited to being directly beneath the horizontal tubular. Furthermore, it takes considerable time to back the bolt out a sufficient distance to clear the full diameter of the tubular of the clamp from the tubular, and then re-advance the bolt for engagement with the tubular particularly when going from a small tubular to a larger one.
The Sure Clamp manufactured by J. R. Clancey is a variation of a C-clamp, and has also been used to mount theater lighting fixtures. The lighting fixture may be initially suspended from a horizontal tubular using this clamp in a short amount of time, although a considerably longer time period is required to secure or tighten the clamp to the tubular. The lighting fixture is lifted vertically to remove the clamp from the tubular in a manner similar to that required for a C-clamp, and accordingly the clamp can only be utilized when sufficient head room above the tubular is provided. Since the clamp does not wrap-around or circumferentially encircle the tubular, it lacks sufficient structural integrity to be safely used to mount fixtures which are relatively heavy as compared to the size and weight of the clamp. Moreover, since the weight of the fixture is used to actuate the clamp, the clamp cannot be easily employed to mount a lighting fixture on inclined or vertical tubulars.
Another type of clamp employed to connect structural tubulars is the Nu-Rail clamp manufactured by Hollander. Crossing tubulars of a grid above a stage may be interconnected by the two separate clamp pieces, which include a pair of dove tail connections. One clamp piece includes a sleeve-like portion for sliding over one tubular, with a dovetail connection projecting from the sleeve-like portion. After the dovetail connections are made, a bolt through the other clamp piece may be tightened to secure the clamp to the second tubular. This type of clamp thus requires a good deal of time and manual dexterity to interconnect the structural tubulars. Moreover, the clamp is intended and may be safely employed on only one size tubular so that the clamp must be disconnected from the lighting fixture, and a new clamp reconnected to the fixture each time the fixture is to be mounted to a different sized tubular.
The need exists for an improved clamp to mount a device, such as a lighting fixture, to structural tubular members. Prior art clamps are difficult and/or time consuming to utilize, often requiring that the operator support the device while the clamp is secured to the tubular. Moreover, prior art clamps do not satisfy safety concerns, either because the clamp does not fully encircle the tubular and thus lacks structural integrity, or because the clamp may allow the suspended fixture to fall from a horizontal tubular before the clamp is tightened to the tubular. While some clamps are not able to mount a device on different sized tubulars, other clamps can only be reliably used to hang a device from a horizontal tubular rather than horizontal, vertical or inclined tubulars.
The disadvantages of the prior art are overcome by the present invention, and an improved clamp is hereinafter disclosed suitable for mounting various devices, such as lighting fixtures, to structural tubular members.